Separation of oils from solids

ABSTRACT

Drill cuttings are cleaned of oil-based drilling mud and oil using a cleansing agent, such as a C6-C10 carboxylic acid, that is preferentially oil soluble at one pH and preferentially water soluble at another pH. The oily cuttings are treated with the carboxylic acid and then washed with an aqueous, alkaline washing solution, which converts the carboxylic acid to its water soluble salt and, with vigorous agitation, lifts most of the oil from the cuttings. In other embodiments, the process is used for cleaning oil-contaminated soil, sand, and gravel, and for separating the oils from the solids in oily sludges.

This application is a continuation, of application Ser. No. 07/621,039,filed Nov. 30, 1990, now is U.S. Pat. No. 5,156,686.

FIELD OF THE INVENTION

This invention relates to the separation of oils from solids, and moreparticularly, to the separation of oils from particulate solids such asdrill cuttings, gravel, sand, soil, and ash. The invention hasapplication, for example, in well drilling operations, in environmentalcleanup of oil spills, and in the reclamation of valuable oil from oilysludges.

INTRODUCTION

The separation of oil from solids is important in a number of fields.The need for effective methods of cleaning spilled oil and fuel fromsand, gravel, and soil is urgent. In addition, drilling operations,particularly offshore operations, frequently employ oil-based drillingfluids which contaminate the drill cuttings. The disposal of drillingfluid-contaminated drill cuttings is ever more strictly regulated, andmethods of cleaning the cuttings for disposal are needed. Finally, theprocessing of alternative energy sources such as oil shale, coal, tarsands, and the like involve the separation of produced oil fromparticulate solids and ash. Methods for cleanly separating oil from suchsolids will provide both recovery of valuable oil products and cleaningof the solids for safer disposal.

SUMMARY OF THE INVENTION

The present invention provides methods for separating oils and greasesfrom solids. In accordance with the invention, an oil phase in contactwith a solid phase is treated with a carboxylic acid that is capable offorming a solution with the oil phase and, preferably, is substantiallyinsoluble in water. The carboxylic acid is then contacted with a reagentthat converts the carboxylic acid to a water-soluble carboxylate saltand with an aqueous washing solution that washes the carboxylate saltand the oil from the solid. Preferably, the reagent is present in thewashing solution, so that conversion of the organic compound to itswater-soluble form and washing of the oil from the solid areaccomplished in one step.

In further embodiments of the invention, the oil and the carboxylic acidare recovered from the used washing solution. In a highly preferredembodiment, oil-based drilling mud, a fluid which comprises both liquidand suspended microparticulate components, is recovered from drillcuttings substantially intact, and the carboxylic acid is recoveredseparately. In this embodiment, when the oil-based mud and carboxylatesalt are washed from the drill cuttings, an oil mud phase spontaneouslyseparates from an aqueous phase containing the dissolved, preferentiallywater-soluble carboxylate salt. The oil mud phase, because it containssuspended microparticulate solids, is heavier than the aqueous phase,and settles beneath the aqueous phase if allowed to stand. The oil mudphase is removed and can be returned to the mud pit for recyclingthrough the well. Then, the pH of the aqueous phase is lowered toconvert the carboxylate salt back to the carboxylic acid. The carboxylicacid, being substantially insoluble in the aqueous phase, separates outas a second, organic phase which can be recovered for recycling in thecleaning process of the invention.

In another embodiment, the oil and carboxylate salt form a weak emulsionin the washing solution. Lowering the pH of the washing solutionconverts the salt back to the carboxylic acid and breaks the emulsion.The oil and carboxylic acid separate out together as an oil phaseadjacent the aqueous phase. The oil phase, which contains the carboxylicacid, can be recovered, for example by simple phase separation, and canbe recycled or incorporated in the feedstock to a refinery as desired.

DETAILED DESCRIPTION OF THE INVENTION

A carboxylic acid useful as a cleansing agent for separating an oil froma solid in the practice of this invention has two desirable properties;namely, the carboxylic acid must be oil-soluble in the acid form, and itmust be convertible to a preferentially water-soluble carboxylate salt.Preferably, the carboxylic acid is preferentially oil-soluble,particularly when the carboxylic acid is to be applied to and dissolvedin the oil on the solid in the presence of free water. A usefulcarboxylic acid is soluble in a cleansing proportion in the oil which isto be separated from a solid. When the carboxylic acid is converted tothe salt form, the salt acts in a manner similar to a weak emulsifier orsurfactant, allowing the oil to be washed away from the solid by anaqueous washing solution.

The carboxylic acid is reversibly convertible between preferentiallyoil-soluble and preferentially water-soluble forms. Thus, bymanipulating the pH of the aqueous washing solution, the carboxylic acidcan be recovered and recycled, improving the economics of the method andminimizing the amount of waste products potentially lost to theenvironment. An example of a reversibly convertible cleansing agentpreferred for use in the invention is n-octanoic acid, also calledcaprylic acid, and its salt, potassium n-octanoate.

As used herein throughout the specification and the claims, the term"preferentially oil-soluble" means more soluble in oil than in water,and the term "preferentially water-soluble" means more soluble in waterthan in oil. Ideally, the carboxylic acid cleansing agent is selected tohave the greatest solvating and penetrating power for the particular oilbeing separated from the oily solids at hand, while remainingwater-soluble in its salt form. As an aid in selecting carboxylic acidsfor use in the invention, the solubility of a candidate acid in No. 2diesel fuel, an arbitrarily chosen representative oil, can be comparedwith its solubility in water, and conversely, the solubility of analkali metal salt of the acid in water can be compared with itssolubility in diesel fuel. It is desirable that the acid be more solublein diesel fuel than in water, preferably by a ratio of at least about 10to 1, and more preferably by a ratio of at least about 50 to 1.Conversely, it is desirable that the salt be more soluble in water thanin diesel fuel, preferably by a ratio of at least about 10 to 1, andmore preferably by a ratio of at least about 50 to 1. The solubilityratios are somewhat arbitrary reference points proposed in an effort toquantify what is intuitively clear to one of ordinary skill in this art;namely, that certain compounds are appreciably soluble in oil but not inwater, and others are appreciably soluble in water but not in oil. Itwill be understood that the solubility of one compound in another isusually a matter of degree.

The carboxylic acids preferred for use as cleansing agents in thepractice of this invention are those which are liquid at ambienttemperatures or at any convenient temperature for using an aqueouswashing solution, i.e., usually between about 0° and about 100° C. Forexample, drill cuttings are often hot when they emerge from a well,sometimes reaching temperatures as high as 80° to 100° C. A carboxylicacid melting at a temperature above 100° C. can also be used to cleanhot drill cuttings if the aqueous washing solution is kept underpressure and maintained at a temperature at or above the melting pointof the carboxylic acid. However, it is preferred to carry out theprocess of the invention under ambient pressure to avoid thedifficulties involved in operating at elevated pressures.

As used herein throughout the specification and the claims, the term"slightly soluble in water" shall mean no more soluble in water thann-butyric acid. This specification discusses a compound or cleansingagent as being convertible between an oil-soluble form and awater-soluble form; it will be understood that this is a figure ofspeech, since actually two different compounds are involved, e.g.,n-octanoic acid and potassium n-octanoate. However, in preferredembodiments of the invention, the two compounds are readily andreversibly interconvertible, so that it can be convenient to speak ofone compound in two forms.

Although normally (i.e., under ambient conditions) liquid carboxylicacids are preferred, non-aqueous liquid solutions of normally solidand/or normally liquid carboxylic acids in suitable non-aqueous solventscan be used, i.e., solvents which also have substantial solvency foroils, and preferably solvents which are miscible with oils. Whether thecarboxylic acid is normally liquid or normally solid, it must bewater-soluble in its salt form.

Carboxylic acids useful in the practice of this invention areasymmetrical in molecular structure, having a substantially hydrophobicend portion in addition to the substantially hydrophilic carboxylic acidend portion, so that their salts can act in a manner similar to that ofsoap and detergent molecules for washing oil from solids with an aqueouswashing solution. The carboxylic acids can be represented by thestructural formula

    R--(COOH).sub.n

wherein n is an integer of at least 1, and R is an organic radical. Whenthe carboxylic acid has more than one carboxylic acid group permolecule, the carboxylic acid groups are preferably asymmetricallyarranged so that the molecule still has a substantially hydrophobic endportion; an example is 3-carboxyoctanoic acid, in which the two carboxylgroups are closer to one end of the molecule than the other. R can bealiphatic or alicyclic, saturated or unsaturated, or aromatic, and canhave inert substituents, i.e., substituents that do not interfere withthe cleansing action of the carboxylic acid and do not react with theoil or solids being treated. R can have from 1 to about 40 carbon atoms,preferably at least 4 carbon atoms, and more preferably at least about 6carbon atoms. R preferably has no more than about 20 carbon atoms, andmore preferably no more than about 12 carbon atoms. Most preferably, Rhas from about 7 to about 11 carbon atoms. Aliphatic monocarboxylicacids are preferred, and of those, carboxylic acids free ofnon-hydrocarbonaceous substituents (other than the carboxyl group) aremore preferred.

Specific examples of useful carboxylic acids include acetic acid,propionic acid, butyric acid, isobutyric acid, valeric acid, isovalericacid, caproic acid, n-heptanoic acid, caprylic acid (i.e., n-octanoicacid), pelargonic acid, capric acid, palmitic acid, stearic acid,arachidic acid, n-heptadecanoic acid, oleic acid, linoleic acid,linolenic acid, arachidonic acid, undecylenic acid, lauric acid,myristic acid, behenic acid, benzoic acid, salicylic acid, bismethylenesalicylic acid, cinnamic acid, pamoic acid, ortho-phthalic acid, andmixtures thereof.

The importance of the two forms of the compound with their differentsolubilities in oil and water can be appreciated in reference to anexample of the process of the invention. Consider the cleaning of drillcuttings coated with oil-based drilling mud. The cleansing agent, in itsoil-soluble form, e.g., caprylic acid, is applied to the cuttings andpenetrates deeply into the layer of oily mud on the cuttings. Thecompound may also be viewed as a penetrating solvent, which penetratesthrough the oil to the solid surface beneath. Sufficient time is allowedfor the cleansing agent to penetrate to the surface of the solidparticles, and preferably, into any oil-filled cracks and pits. Then,the treated cuttings are contacted under vigorous agitation with theaqueous washing solution containing a reagent, e.g., potassiumhydroxide, that converts the cleansing agent to its water-soluble form,potassium caprylate. The cleansing agent, now water-soluble, rinses offthe solid particles, loosening and carrying away the oil mud. Becausethe cleansing agent, in its oil-soluble form, can penetrate to thesurface of the solid particles, the particles are thoroughly cleaned ofoil mud and are substantially free of residual base oil.

Now, the importance of reversible convertibility of the cleansing agentbetween its two forms can be seen. After separation from the cuttings byscreening or the like, the wash water contains the dissolved carboxylatesalt and weakly emulsified or suspended globules of the oil mud removedfrom the cuttings. The oil mud can be allowed to separate by gravity or,preferably, is separated from the wash water in a hydroclone. Then, asuitable reagent, e.g., hydrochloric acid, is added to the wash water toconvert the carboxylate salt back to the water-insoluble carboxylicacid, which then forms a separate layer on top of the wash water. Thecleansing agent is thus recovered for recycling in the process of theinvention. Therefore, it is preferred that the carboxylic acid itselfhave little or no solubility in water, i.e., no more solubility in waterthan caprylic acid (n-octanoic acid). The wash water, now containingpotassium chloride, can be recycled in the process of the invention.

The present invention is directed broadly to the separation of oils andoil-containing phases from solids. As used herein throughout thespecification and the claims, the term "oil" means ahydrocarbon-containing material that is (a) substantially insoluble,i.e., less than 0.1 weight percent by weight of solution, in water at 20° C., and (b) appreciably soluble, i.e., more than 1 weight percent byweight of solution, in liquid caprylic acid at any temperature betweenthe melting point and the boiling point of caprylic acid, i.e., betweenabout 16° C. and about 238° C. Because dilute aqueous acid and alkalisolutions are also employed in the process of this invention, it ispreferred that an oil to be treated in accordance with this invention besubstantially insoluble in such dilute aqueous acids and alkalis.Furthermore, it is preferred that the oil be soluble in liquid caprylicacid to the extent of at least about 10 weight percent, and morepreferably at least about 25 weight percent, by weight of solution.Ideally, the oil is freely miscible with liquid caprylic acid.

An oil that can be separated from a solid in accordance with thisinvention can comprise natural or synthetic oils, fats, greases, orwaxes, including those derived from animal, vegetable, or mineralsources; synthetic oils and greases containing hydrocarbon groups, suchas organopolysiloxanes (silicones); and mixtures thereof. The oiltypically comprises a substantially hydrocarbonaceous oil or grease,usually a natural or synthetic petroleum or petroleum product, such ascrude oil, heating oil, bunker oil, kerosene, diesel fuel, aviationfuel, gasoline, naphtha, shale oil, coal oil, tar, lubricating oil,motor oil, solvents, waxes, and lubricating greases.

The solid phase from which an oil phase is separated in accordance withthis invention is usually substantially insoluble in the carboxylicacid, e.g., caprylic acid, water, and dilute aqueous acids and alkalisunder the conditions employed in the practice of this invention. Thesolid phase can comprise an article of manufacture, such as a metal partor glass plate which is being cleaned of oil and grease. More often, thesolid phase comprises particulate solids. The solid phase can compriseinsoluble organic materials, e.g., cellulosic materials such as bark,straw, or sawdust. Preferably, the solid phase comprises a majorproportion of inorganic material, such as rocks, gravel, drill cuttings,sand, soil, or ash.

The oil phase can also comprise other dissolved or suspendedconstituents, including suspended solid constituents which remain partof the oil phase after separation from another solid phase. For example,oil-based drilling fluid typically comprises a base oil, additives suchas surfactants and viscosity modifiers, and suspended particles of clay.The clay imparts body to the fluid so that the circulating fluid canentrain drill cuttings and carry them from the borehole. Drilling fluidsalso frequently contain a finely divided weighting material such asbarite, a dense mineral that increases the density of the fluid for usein deep wells. Both the clay and the weighting material are typically sofinely divided that they can remain suspended in the base oil for asubstantial length of time. In the separation of drilling fluid fromdrill cuttings in accordance with this invention, the drilling fluid,including its suspended solid constituents, can constitute the "oilphase" and the drill cuttings can constitute the "solid phase."

Whether a given particulate solid can be separated from an oil phase inaccordance with this invention is believed to depend in part upon theaffinity of the oil for the solid, that is, upon the tendency of the oilto wet the solid, and also in part upon the particle sizes of the solid,larger particles being easier to separate. For example, the base oil indrilling fluid has a relatively strong affinity for the clay particles,whereas shale oil has a lesser affinity for the siliceous ash particlesfound in shale oil deasher sludge. The clay, e.g., bentonite, particlesin drilling fluid are extremely fine, about 0.05 to 5 microns, averagingabout 0.5 microns, whereas the ash particles in deasher sludge are onthe order of 100 times larger, about 0.5 to 200 microns, averaging about50 microns. In addition, clay particles are electrically charged andhence have a high affinity for oil, whereas siliceous particles areelectrically neutral and hence have a lower affinity for oil. Thus, inone embodiment of this invention, clay particles in drilling fluidremain with the base oil when the fluid is separated from the drillcuttings, whereas in another embodiment, ash particles are separatedfrom shale oil.

It is not possible to state in advance for all possible combinations ofoils and particulate solids precisely which mixtures can be successfullyseparated in accordance with this invention. As a general rule, however,particles ranging in average size (greatest cross-sectional dimension)from about 50 microns and larger can be separated from hydrocarbonaceousoils, such as crude and refined petroleum oils and similar oils producedfrom oil shale, tar sands, coal, and the like, without difficulty by themethods of this invention. A simple laboratory-scale test such as thatdescribed in Example 3 will quickly show whether a given mixture can beseparated in accordance with this invention.

Once the mixture of oil and solids to be separated has been treated withthe carboxylic acid cleansing agent, the carboxylic acid is converted tothe corresponding carboxylate by contacting the acid with a base, suchas an alkali metal or ammonium hydroxide, carbonate, or bicarbonate.Alkali metal hydroxides are preferred. Usually, sodium hydroxide is mostpreferred because of its low cost.

However, potassium hydroxide is most preferred for use in separatingoil-based drilling fluid from drill cuttings containing water-sensitiveshale. Most wells of any appreciable depth pass through strata ofwater-sensitive shale, one reason oil-based drilling fluids arepreferred for deep wells. In aqueous media, such shale tends to crumbleand disperse into very fine particles. If shale in drill cuttings ispermitted to disperse in the aqueous washing solution used in theprocess of this invention, the resulting fine particles can be difficultor impossible to separate from the drilling fluid. Potassium ion in theaqueous washing solution tends to inhibit such dispersion of shale. Forthis purpose, it is desirable to maintain a potassium concentration,calculated as KCl, of at least about 1 weight percent, preferably atleast about 2 percent, and more preferably at least about 4 percent, andeven more preferably at least about 6 percent, in the aqueous washingsolution. In the presently most preferred embodiment, the aqueouswashing solution contains about 5 weight percent potassium chloride.Concentrations higher than about 10 percent can be used, but usually donot provide any significant advantage.

Whichever base is used; sufficient base is introduced to convert atleast some, and usually at least a major proportion, of the carboxylicacid present in the treated mixture to the carboxylate salt. Preferably,sufficient base is introduced to convert substantially all of thecarboxylic acid to the salt, i.e., one equivalent of base per equivalentof acid. The addition of base can be regulated by monitoring the pH ofthe aqueous washing solution during addition of the base. When the pHcrosses above 7 and begins to climb, sufficient base has been added.Usually, when addition of base is complete, the aqueous solution has apH of at least about 8, preferably between about 9 and about 12, whichindicates that a slight excess of base has been added. The addition ofany greater excess of base provides little or no benefit, but needlesslyincreases the consumption of the acid used subsequently to neutralizethe aqueous solution and convert the carboxylate salt back to thecarboxylic acid form.

The ratio of aqueous washing solution to separable oil phase in themixture being separated is selected to provide a good balance of processconditions. If too little washing solution is used, separation of theoil phase from the solid may be incomplete, and the resulting emulsionof aqueous and oil phases may be tight and viscous, and thus hard tobreak or separate. If much more washing solution than necessary is used,larger equipment will be needed to handle the larger volume of liquidand costs will thus be increased. Usually, a sufficient ratio of washingsolution to oil phase is used to produce a weak or unstable emulsion ofoil phase in the washing solution that is physically manageable suchthat, when the emulsion breaks, the two phases can separate readily bygravity or be separated with the use of a simple liquid-liquid phaseseparator such as a hydroclone.

As mentioned above, it is preferable to use a stoichiometric amount ofbase plus a slight excess to neutralize the carboxylic acid in a givenquantity of treated oil/solid mixture and convert it to thecorresponding salt. Further, the volume of washing solution used to washthat quantity of oil/solid mixture is selected to provide a desirablebalance between manageability of the resulting washing solution/oilphase mixture and the total volume of liquid to be handled. It followsthat, when the base is included in the washing solution, rather thanbeing introduced separately, the concentration of base in the washingsolution is determined by the two factors just mentioned. In otherwords, the concentration of base in the washing solution, taken byitself, is not usually controlled independently.

When the mixture of oil-contaminated solids and carboxylic acid and/orcarboxylate salt is contacted with the aqueous washing solution, it isdesirable to provide sufficient agitation, i.e., sufficient shear, toassist in the removal of the oil phase from the solids. The need foragitation, and the degree of agitation or shear required, are related tothe kind of oil/solid mixture being separated. When a light oil such askerosene is separated from a siliceous solid such as sand, adequateseparation can be achieved with little or no agitation of the carboxylicacid treated mixture in the aqueous wash. When heavier oils, such asheavy crude oil or oil-based drilling mud, are to be separated fromirregular, clay-containing particles such as drill cuttings, sufficientagitation and shear are required to strip the oil from the solids by acombination of the mechanical action of the shear and the chemical,detergent-like action of the carboxylate salt. The oil is thus entrainedin the aqueous wash and carried away from the solids. The aqueous washwith entrained oil can have the appearance of an unstable or weakoil-in-water emulsion, but typically the oil droplets coalescespontaneously into a continuous oil phase when the mixture is allowed torest or is passed through a phase separator such as a hydroclone.

In its broadest aspect, the process of the invention comprises the stepsof: treating a system having an oil phase and a solid phase with acarboxylic acid cleansing agent that is soluble in the oil phase fordissolving cleansing agent in the oil phase; contacting the treatedsystem, preferably with vigorous agitation, with an aqueous washingsolution containing a reagent that converts the cleansing agent to apreferentially water-soluble, oil-insoluble form; and separating thewashing solution and at least a portion of the oil phase from the solidphase. Thus, the present invention provides methods for separatingorganic liquids from solids.

Briefly, a method of the invention comprises the steps of dissolving acleansing agent in an oil phase which is in contact with a solid phase;contacting said oil phase with an aqueous washing solution forseparating at least a portion of said oil phase from said solid phase,said washing solution comprising a reagent which converts said cleansingagent from a preferentially oil-soluble form to a preferentiallywater-soluble form; and separating said washing solution and saidportion of said oil phase from said solid phase.

The proportion of cleansing agent to use is not critical, in that almostany amount above a trace will provide some benefit.

Usually, the cleansing agent is a liquid comprising a carboxylic acid,preferably a liquid carboxylic acid, and, optionally, an auxiliarysolvent for oils and greases. In general, a sufficient amount of thecleansing agent is applied to wet all of the contaminated surfaces to becleaned. When a particulate solid is being cleaned, sufficient cleansingagent can be used to substantially fill the void volume in a mass of theparticles; in other words, enough is used to cover the mass. Largerproportions of cleansing agent can be used, especially for heavilycontaminated materials or materials contaminated with heavy oils, tars,or greases. Smaller proportions of cleansing agent can be used,particularly for lightly contaminated solids, if adequate mixing isprovided to distribute the cleansing agent onto the contaminatedsurfaces.

Alternatively, the cleansing agent is used in a proportion such that thecarboxylic acid present is equal to at least about 10 percent by volumeof the oil and grease to be removed from the solids, preferably at leastabout 25 percent, more preferably at least about 50 percent, and evenmore preferably at least about 100 percent by volume.

Cleaning Drill Cuttings

In a preferred embodiment of the invention, drill cuttings from a welldrilling operation using an oil-based drilling fluid, or mud, arecleaned of mud and oil sufficiently for environmentally safe disposal.The cleaned cuttings are essentially nontoxic and can be disposed of onland without the need for the special procedures required for disposalof toxic waste.

In many offshore drilling operations when an oil-based drilling mud hasbeen used, environmental protection has made it necessary to accumulatethe drill cuttings and transport them to shore for disposal in a toxicwaste site. This can be a significant element of expense in the totalcost of the well. Thus, in a highly preferred embodiment of theinvention, drill cuttings from an offshore well are cleaned of drillingmud and oil in accordance with the invention and are returned to the seanear the offshore drilling platform. It is estimated that this procedurecan result in a cost saving on the order of a million dollars for atypical North Sea oil well.

Regulatory standards vary. The United Kingdom has had a limit of 15weight percent, and is proposing a limit of 10 percent, oil residue oncuttings (dry weight basis) discharged into the sea. Other countries,e.g., Norway and Holland, already have a limit of 10 weight percent,which is likely to be substantially reduced in the near future. TheUnited States requires that cuttings discharged to the sea be"non-sheening," meaning that the cuttings do not leave an oily sheen onthe surface of the water; this corresponds to a hydrocarbon residue onthe cuttings of less than about 10 percent by weight of dry, oil-freecuttings.

The methods of this invention can remove at least about 75 weightpercent of the oil mud clinging to drill cuttings, preferably at leastabout 90 percent, and most preferably at least about 95 percent. Thepentane-extractable residual oil (hydrocarbon) on the cuttings can bereduced to less than about 5 percent by weight of dry, oil-freecuttings, preferably less than about 2 percent, and more preferably lessthan about 1 percent.

An example of a commercial-scale, continuous process for cleaning drillcuttings is described. Oily cuttings and liquid carboxylic acid, mostpreferably a 50:50 blend of caprylic and capric acids, are fed into amixer, where the carboxylic acid dissolves, and dissolves in, the oilmud on the cuttings. The blend remains liquid at lower temperatures thaneither acid alone. The resulting slurry is fed to an extractor, where itis combined with an aqueous wash solution containing KOH and 5% KClrecycle from the regenerator (described below) to provide an overall KOHconcentration of 4%. The KOH reacts with the carboxylic acid, convertingit to its water-soluble potassium salt. Usually, sufficient alkali isused so that the aqueous phase has a final pH above 7, e.g., above about7.5 or more, assuring substantially complete conversion of thecarboxylic acid. The extractor provides sufficiently high shear to stripthe oil mud and carboxylate salt from the cuttings, forming a suspensionor weak, unstable emulsion of oil mud globules in the aqueous washsolution. At the same time, the carboxylate salt, which ispreferentially water-soluble, passes into the aqueous phase.

The slurry, now containing the drill cuttings in a suspension orunstable emulsion of oil mud in wash solution, is then transferred to avibrating screen, where the liquid phase (oil mud and wash solution)drains off. Water is sprayed on the cuttings from above to further rinsethe oil mud and wash solution from the cuttings through the screen. Fromthe screen, the cuttings are moved by a screw conveyor to a collectionpoint for return to the sea or shipment for onshore disposal.Alternatively, the final rinse water can be sprayed on the cuttings asthey move through the screw conveyor. The cleaned cuttings can then bedisposed of by the same methods used for cuttings from wells drilledwith the use of water-based drilling fluid, e.g., returning cuttings tothe sea or burying them in pits on land.

The underflow is pumped to a separator, where the oil mud globulessettle to the bottom because of their high density, which isattributable to the weighting material and clay contained in the mud.Preferably, the separator is a hydroclone, which provides faster andmore complete separation than gravity alone. The oil mud globulescoalesce into a continuous oil mud phase, which can be drained off andrecycled to the active mud system to offset the cost of building newmud.

The supernatant aqueous phase containing dissolved potassium carboxylatesalt is transferred to a regenerator, where HCl is added to regeneratethe carboxylic acid. The carboxylic acid, being insoluble or onlyslightly soluble in water, separates out as an organic phase on top ofthe aqueous phase and is recycled to the mixer to be combined withincoming contaminated drill cuttings.

The aqueous phase from the regenerator, now containing 5 percent KCl asa result of the reaction between the HCl and the potassium carboxylatesalt, is recycled back to the extractor as part of the aqueous washsolution.

Large amounts of lime (Ca(OH)₂) in the mud system, i.e., more than about2 pounds per barrel, are best avoided, because excess lime will cause ahigh pH and react with the carboxylic acid, thickening the mud. This isnot a problem, however, because oil-based muds do not usually requirelarge proportions of lime (a source of free Ca++ ion needed to activatesome emulsifiers). CaCl₂, which is normally included in oil muds, willoften provide a sufficient source of Ca++ ion. Alternatively,emulsifiers can be used which do not require lime to be activated.

The properties of oil mud recovered from cuttings in accordance withthis invention are not significantly adversely affected. The recoveredmud can be returned to the active mud system without danger to theproperties thereof.

Environmental Cleanup

The present invention is especially useful for cleaning rock, gravel,sand, and soil that is contaminated with crude oil, grease, and/orpetroleum products such as gasoline, diesel fuel, and fuel oil as aresult of oil spills, pipeline breaks, leaking fuel tanks, industrialoperations, and the like. In an embodiment of the invention,contaminated material is excavated, passed through the cleaning process,and returned to the site of origin. If the highest degree of cleaning isdesired, material first cleaned in accordance with this invention is inexcellent condition to be treated by one of the known biological methodsfor final purification. The present invention can quickly remove most ofthe contaminating oil, grease, or fuel, and leaves only a small residueof the cleansing agent, which is itself readily biodegradable and canpromote the growth of the microorganisms that degrade any residualtraces of the contaminants.

In another embodiment of the invention, the cleansing agent is appliedto a contaminated surface, such as rock, a seawall, pavement, and thelike. The treated area is then washed with the aqueous washing solutionfor removal of the contaminating grease or oil. Preferably, the usedwashing solution is captured so that the oil or grease and the cleansingagent can be recovered for reuse or safe disposal.

Treatment of Shale Oil Deasher Sludge

Oil shale is a sedimentary rock containing solid organic matter calledkerogen. By a variety of techniques, oil shale is fragmented andretorted to break down the kerogen into gaseous and liquidhydrocarbonaceous products, including shale oil. The shale oil thusproduced contains a substantial proportion of ash, i.e., finely divided,predominantly siliceous, particulate matter. The ash must be removed torender the shale oil fit for further processing.

One method for removing ash from shale oil involves washing the oil withwater. After a series of steps such as de-emulsification andcentrifuging, the solids become concentrated in a sludge containing freewater and an emulsion of shale oil, solids, and water. A representativesample of such a sludge contains, after decanting any free water phase,about 50 percent water, 30 percent oil, and 20 percent solids. Becauseof its oil content, the sludge must be handled as a toxic wasterequiring special disposal techniques. In addition, recovery of the oiltrapped in the sludge can result in several million dollars per year ofadditional oil production from a single commercial oil shale retort.

In accordance with this invention, shale oil deasher sludge can betreated so as to recover a high percentage, e.g., at least about 90percent, preferably at least about 95 percent, and more preferably atleast about 99 percent of the shale oil, leaving the solidssubstantially non-toxic for safe disposal without special precautions.Example 3 illustrates the treatment of shale oil deasher sludge inaccordance with this invention.

In another embodiment, sufficient liquid carboxylic acid is mixed withthe sludge to reduce the viscosity thereof, so that the ash particlescan settle out by gravity or in a continuous centrifuge, for example.The shale oil, now free of ash, can be treated with an alkali wash,preferably low-cost aqueous NaOH, for extraction of the carboxylic acidas the sodium carboxylate salt. The concentrated ash can then be treatedseparately with the aqueous alkali wash, preferably with vigorousagitation, for removal of the residual shale oil/carboxylic acid mixturepresent in the ash. The used wash solutions, which contain sodiumcarboxylate, can be combined in a regenerator and treated with HCl forregeneration of the carboxylic acid.

Other finely-divided, oil-contaminated solids can be treated in thisway, such as refinery sludges, soils from refinery and industrial sites,soils from the site of leaking fuel storage tanks, and the like.

The following examples are intended to illustrate particular embodimentsof the invention. The examples are not intended in any way to limit theinvention, the scope of which is defined in the appended claims.

EXAMPLE 1

Four cuttings cleaning processes were compared in laboratory-scaletests: carboxylic acid method, base oil dilution (with Conoco LVT oil),ether-alcohol wash, and surfactant wash. The cuttings were obtained froman offshore well near Texas. Milpark Carbo-Drill diesel oil-based mudwith an oil-water ratio of 80:20 was used on this well. The compositionof the mud is given in Table 1 along with the toxicity of No. 2 diesel.The formation which was drilled consisted primarily of gumbo shale. Thishighly reactive shale contains mostly clay. Generic descriptions of thechemicals used in the cleaning tests are provided in Table 2.

                  TABLE 1                                                         ______________________________________                                        COMPOSITION OF OIL-BASED DRILLING MUD                                         AND TOXICITY OF DIESEL OIL                                                    Component                Quantity                                             ______________________________________                                        15 LB/GAL OIL-BASED DRILLING MUD                                              No. 2 Diesel Oil         .615   bbls                                          Carbo-Mul (Primary Emulsifier)                                                                         5.8    lbs/bbl                                       Carbo-Tec L (Secondary Emulsifier)                                                                     5.0    lbs/bbl                                       25% CaCl.sub.2 Brine     .109   bbls                                          Barite (Weighting Material)                                                                            405.0  lbs/bbl                                       Carbo-Gel (Organophilic Clay)                                                                          2 2.0  lbs/bbl                                       Lime (Ca(OH).sub.2)      2.0    lbs/bbl                                       Carbo-Trol A-9 (Fluid Loss Control Agent)                                                              2.0    lbs/bbl                                       TOXICITY OF NO. 2 DIESEL                                                      Toxicity: Mysid Shrimp 96 hr. LC.sub.50, % SPP*                                                        <1                                                   ______________________________________                                         *Percentage of SPP (suspended particulate phase prepared by shaking a 1:9     mixture of drilling fluid base oil and sea water) required to kill 50% of     Mysidopsis bahia organisms after 96 hours (EPA standard). A low LC.sub.50     values implies high toxicity.                                            

                  TABLE 2                                                         ______________________________________                                        GENERAL DESCRIPTIONS OF CUTTINGS                                              WASHING CHEMICALS                                                                            Generic Description                                            ______________________________________                                        1.    Carboxylic Acid                                                                              Octanoic acid or caprylic                                                     acid (a C.sub.8 carboxylic acid                                               derived from                                                                  vegetable oil).                                          2.    LVT Oil        A petroleum base oil with a                                    (Conoco)       distillation range of                                                         367-505° F., 14% aromatics                                             and a low toxicity relative                                                   to diesel.                                               3.    Ether-Alcohol  Methoxytriglycol.                                        4.    Anionic Surfactant                                                                           Sodium dodecyldiphenyl                                         (Dowfax 2A1)   oxide disulfonate (45%                                                        active)                                                  ______________________________________                                    

The following procedure was used in the cleaning method of thisinvention:

1. 20 gms of mud-contaminated cuttings were placed in a 100 cc graduatedcylinder;

2. 5 mls of caprylic acid were added to the cuttings;

3. The sample was shaken for 3 minutes;

4. 30 mls of 2.5% KOH+6% KCl were added (resulting pH=13);

5. The sample was shaken for 3 minutes;

6. The resulting slurry was poured over a 400 mesh screen (0.0015 inchopening) with vacuum on (a 140 mesh screen with 0.0041 inch opening wasused in a repeat test);

7. The cuttings on the screen were rinsed with 30 mls of 2.5% KOH+6%KCl; and

8. The oil mud and caprylic acid were regenerated by adding 12 mls of 6NHCl to the wash solution (resulting pH=5).

Similar procedures were used for the LVT base oil dilution,ether-alcohol wash, and surfactant wash tests. The primary difference inthese tests was that pH adjustment with KOH and HCl was not used.

After each test, the hydrocarbon extraction efficiency was determinedusing pentane (see Table 3 for an example calculation).

                  TABLE 3                                                         ______________________________________                                        EXAMPLE CALCULATION OF EXTRACTION                                             EFFICIENCY (Test #3, Ether-Alcohol)                                           ______________________________________                                        1.   Test sample consists of gumbo shale drill cuttings                            coated with oil mud. These cuttings were obtained                             from an offshore well near Texas. A 20.2 gm test                              sample contains, on average, 17.5 gms of gumbo shale                          cuttings coated with 2.6 gms of oil mud, as determined                        on a representative sample by pentane extraction.                        2.   Weight of 20.2 gm test sample after extraction with                           ether-alcohol = 19.3 grams.                                              3.   Weight of material extracted by ether-alcohol =                               20.2 - 19.3 = 0.9 gms.                                                   4.   Weight of sample after pentane extraction (to                                 determine residual oil mud on cuttings after                                  ether-alcohol extraction) = 17.4 gms.                                    5.   Weight of additional material extracted by pentane =                          19.3 - 17.4 = 1.9 gms.                                                   6.   Total weight of material removed by ether-alcohol                             followed by pentane extraction = 0.9 + 1.9 = 2.8 gms.                    7.   Extraction efficiency using ether-alcohol* =                                   ##STR1##                                                                ______________________________________                                         *Note: The test specimen apparently contained 2.8 gms of extractable          material as compared with 2.6 gms on the representative sample mentioned      above. The difference was probably due to dispersed gumbo shale passing       through the 400 mesh screen in test #3.                                  

The extraction efficiencies from the cuttings washing tests are shown inTable 4.

                  TABLE 4                                                         ______________________________________                                        RESULTS OF CUTTINGS WASHING TESTS                                                        WT. % OIL MUD                                                                 EXTRACTED* (of  EXTRACTED OIL                                                 original oil mud on                                                                           MUD RECOVER-                                       Process    cuttings)       ABLE ?                                             ______________________________________                                        1.  FATTY      92.3 (400 mesh screen)                                                                        YES                                                ACID                                                                          6% KCl,    98.0 (140 mesh screen)                                                                        YES                                                2.5% KOH                                                                  2.  LVT OIL,   50.0 (400 mesh screen)                                                                        YES                                                6% KCl                                                                    3.  ETHER-     32.0 (400 mesh screen)                                                                        YES                                                ALCOHOL,                                                                      WATER                                                                     4.  ANIONIC    68.0 (400 mesh screen)                                                                        NO                                                 SURFAC-                                                                       TANT,                                                                         6% KCl                                                                    ______________________________________                                         *Oil mudcontaminated cuttings originally contained 13 wt. % oil mud as        determined by pentane extraction.                                        

The carboxylic acid method extracted much more Oil mud from the cuttings(92-98 wt. %) than any of the other three methods (50 wt. % for the LVToil dilution, 32 wt. % for the ether-alcohol wash and 68 wt. % for thesurfactant wash). The extraction efficiency obtained in the carboxylicacid test was slightly greater using a 140 mesh screen (98.0 wt. %) thana 400 mesh screen (92.3 wt. %), possibly due to dispersed shale passingthrough the 140 mesh screen or oil mud being retained on the 400 meshscreen. The extracted oil mud and caprylic acid were recovered by adding12 ml of 6N HCl to the filtrate (spent wash solution). After theextraction, the cuttings were observed to be clean and free of oil mud.They exhibited a slight odor of carboxylic acid but no diesel oil odor.The 2-8% "unextracted" residue was probably not oil mud but insteadcarboxylic acid salt left over from the washing step.

The poor extraction efficiency with LVT oil (50 wt. %) in the secondtest was due to failure of the LVT oil to completely wash off thecuttings. This was confirmed by noting an oily odor on the washedcuttings. Neither ether-alcohol nor anionic surfactant penetrated veryfar into the oil mud on the cuttings, hence the poor extractionefficiencies (32% and 68%, respectively). Observation of the cuttingsafter these tests indicated that a significant amount of oil mudremained on the cuttings. After the anionic surfactant wash, the oil mudcould not be recovered in the filtrate because it was tightlyemulsified.

EXAMPLE 2

The four solids cleaning processes described in Example 1 were carriedout on 20×40 mesh silica sand contaminated with about 10 wt. % kerosene.The kerosene contained a green oil-soluble dye for visual identificationof residual kerosene on the sand.

The following procedure was used in the carboxylic acid method:

1) 18 gms of sand contaminated with 2 gms of kerosene were placed in a100 cc jar;

2) 5 mls of caprylic acid were added to the sand

3) the sample was shaken for 3 minutes;

4) 30 mls of 2.5% KOH were added (resulting pH=13)

5) the sample was shaken for 3 minutes;

6) the resulting slurry was poured over a 140 mesh screen (0.0041 inchopening);

7) the sand on the screen was rinsed with 40 mls of 2.5% KOH;

8) the kerosene and caprylic acid were regenerated by adding 12 mls of6N HCl to the wash solution (resulting pH=5).

Similar procedures were used for the LVT oil dilution, ether-alcoholwash and surfactant wash tests. The primary difference in these testswas that pH adjustment with KOH and HCl was not used.

After each test, the hydrocarbon extraction efficiency was determinedusing pentane. The extraction efficiencies from the sand washing testsare shown in Table 5.

                  TABLE 5                                                         ______________________________________                                        RESULTS OF SAND WASHING TESTS                                                 (20 × 40 mesh sand coated with 10 wt. % kerosene)                                      Wt. % Kerosene                                                                Extracted     Extracted                                                       (of original  Kerosene 100%                                    Process        kerosene on sand                                                                            Recoverable?                                     ______________________________________                                        1.  Carboxylic Acid,                                                                             100           Yes                                              2.5% KOH                                                                  2.  LVT Oil, Water 85            Yes                                          3.  Ether-Alcohol, Water                                                                         57            No                                           4.  Anionic Surfactant,                                                                          95            No                                               Water                                                                     ______________________________________                                    

The method of this invention extracted more kerosene from the sand (100wt. %) than any of the other three methods (85 wt. % for the LVT oildilution, 57 wt. % for the ether-alcohol wash, and 95 wt. % for thesurfactant wash). After extraction by the process of this invention, thesand was observed to be clean and free of kerosene odor and green colorfrom oil-soluble dye. The extracted kerosene was decanted from theaqueous phase. Then, the caprylic acid was recovered by adding 12 ml of6N HCl to the remaining filtrate (spent wash solution).

The LVT oil did not completely wash off the sand. This was confirmed bynoting an oily odor and a green color on the sand from the oil-solubledye. The kerosene and LVT oil in the spent wash solution completelyseparated from the aqueous phase.

In the third test, the ether-alcohol did not sufficiently penetrate theoil nor did it completely wash off the sand. The inability to wash offthe sand is undesirable because of the high toxicity of ether-alcohol.Most of the kerosene in the spent wash solution was recoverable.However, some cross-contamination of kerosene and ether-alcoholoccurred.

The extraction efficiency with anionic surfactant in the fourth test washigh (95 wt. %), however, the kerosene was not recoverable in the spentwash solution because of emulsification.

EXAMPLE 3

Two shale oil deasher sludge cleaning processes were compared inlaboratory-scale tests: the method of the present invention and naphthaaddition.

The following procedure was used to treat shale deasher sludge withcarboxylic acid:

1) 3.5 gms sludge was mixed with 3.5 gms carboxylic acid;

2) the sample was stirred for 5 minutes;

3) the sludge and carboxylic acid were poured into a buchner funnel (7cm i.d.) containing Whatman No. 1 filter paper. A 100-ml filter flaskconnected to vacuum was placed beneath the funnel to collect filtrate;

4) after filtering for 5 minutes, 35 mls 2.5% NaOH was used to rinse thefilter cake;

5) shale oil was decanted from the surface of the filtrate;

6) concentrated (6N) HCl was added to the filtrate to regeneratecarboxylic acid. The carboxylic acid was decanted from the surface ofthe filtrate;

7) the filter cake was weighed to determine recovery efficiency;

8) the test was repeated using a 2:1 ratio of carboxylic acid to deashersludge (7 gms of carboxylic acid and 70 mls 2.5% NaOH).

The following procedure was used to treat shale deasher sludge withnaphtha:

1) 3.5 gms sludge was mixed with 3.5 gms naphtha;

2) the sample was stirred for 5 minutes;

3) the sludge and naphtha were poured into a buchner funnel (7 cm i.d.)containing Whatman No. 1 filter paper. A 250-ml filter flask connectedto vacuum was placed beneath the funnel to collect filtrate;

4) After filtering for 5 minutes, the filter cake was weighed todetermine recovery efficiency;

5) the test was repeated using a 2:1 ratio of naphtha to deasher sludge(7 gms naphtha).

The shale oil recovery efficiencies obtained in the laboratory tests areshown in Table 6. The carboxylic acid process extracted significantlymore shale oil (97.2 wt. %) than the naphtha addition (62.5 wt. %) whena 1:1 ratio of treating agent to deasher sludge was used. When a 2:1ratio was used, the carboxylic acid also exhibited higher extractionefficiency than naphtha addition (99.6 wt. % versus 74.4 wt. %). In acommercial process, a 2:1 ratio would be preferred because half thematerials could be used with about the same results.

                                      TABLE 6                                     __________________________________________________________________________    RESULTS OF SHALE DEASHER SLUDGE CLEANING EXPERIMENTS                          USING FATTY ACID AND NAPHTHA TREATING AGENTS                                           Wt.   Wt. Sludge           Is Shale Oil                                       Untreated                                                                           After % Recovery     In Spent                                  Treating Sludge,                                                                             Treatment,                                                                          of Shale       Wash Solution                             Agent    gms   gms   Oil & Water*   Recoverable?                              __________________________________________________________________________    1:1 Treating Agent:Sludge Ratio                                               Carboxylic Acid                                                                        3.5    .73                                                                                 ##STR2##      Yes, immediately                          Naphtha  3.5   1.72                                                                                 ##STR3##      Yes, after distillation                   2:1 Treating Agent:Sludge Ratio                                               Carboxylic Acid                                                                        3.5    .66                                                                                 ##STR4##      Yes, immediately                          Naphtha  3.5   1.38                                                                                 ##STR5##      Yes, after distillation                   __________________________________________________________________________     *pentane-extractable                                                          **weight of shale oil and water as determined previously by pentane           extraction on a representative sample of deasher sludge                  

In the naphtha addition tests, it was not possible to distinguishbetween unextracted shale oil and naphtha which was left behind on thesolids (filter cake). Undoubtedly, a significant part of the"unextracted shale oil" was actually naphtha. Since naphtha is a highervalue product when raw shale oil, this is detrimental to the economicsof the process.

All of the extracted shale oil was recovered from the spent washsolution in the carboxylic acid test. After decanting the shale oil, 6NHCl was added to lower the pH, return the carboxylic acid to itsoil-soluble form, and recover it by decanting. In the naphtha test, theshale oil and naphtha in the spent was solution could not be separatedwithout using an expensive distillation step (which requires a largequantity of heat).

After the carboxylic acid extraction, the solids were observed to beclean and free of shale oil. The 0.4-2.8% "unextracted" residue wasprobably mostly carboxylic acid salt left behind during the washingstep. From an environmental standpoint, it is much more desirable toleave behind a residue of vegetable-based carboxylic acid than toxicnaphtha (containing 12-13% benzene) and raw shale oil.

While particular embodiments of the invention have been described andillustrated herein, it will be understood that the invention is notlimited thereto, since many obvious modifications can be made. Thisinvention is intended to include any such modifications as will fallwithin the scope and equivalency of the appended claims.

What is claimed is:
 1. A method for cleaning drill cuttings contaminatedwith oil-based drilling fluid in a well drilling operation, whichcomprises:contacting contaminated cuttings with a liquid compositioncomprising a carboxylic acid; then washing the cuttings with an aqueouswash comprising a base for converting the carboxylic acid to awater-soluble carboxylate salt; and removing an aqueous phase containingcarboxylate salt and entrained drilling fluid.
 2. The method of claim 1further comprising the steps of:separating the entrained drilling fluidfrom the aqueous phase; and then adding an acid to the aqueous phase forregenerating the carboxylic acid.
 3. A method for cleaning a mixturecomprising drilling cuttings contaminated with an oil-based drillingmud, the method comprising the steps of:(a) contacting the mixture witha carboxylic acid; (b) contacting the carboxylic acid-containing mixtureformed in step (a) with a reagent capable of converting the carboxylicacid to a water-soluble carboxylate salt; (c) contacting the carboxylatesalt-containing mixture formed in step (b) with an aqueous washingsolution; (d) separating a solid phase comprising at least some of thedrill cuttings present in the carboxylate salt-containing mixture from aliquid phase comprising at least some of (i) the carboxylate salt and(ii) the oil-based drilling mud present in the carboxylatesalt-containing mixture and (iii) the water present in the aqueouswashing solution; and (e) separating an oil phase comprising at leastsome of the oil-based drilling mud present in the liquid phase from anaqueous phase comprising at least some of the carboxylate salt and waterpresent in the liquid phase, the oil phase being denser than the aqueousphase.
 4. The method of claim 3 wherein the oil phase is separated fromthe aqueous phase in step (e) by removing the oil phase from beneath theaqueous phase.
 5. A method for cleaning a mixture comprising drillingcuttings contaminated with an oil-based drilling mud, the methodcomprising the steps of:(a) contacting the mixture with a carboxylicacid; (b) contacting the carboxylic acid-containing mixture formed instep (a) with an aqueous base solution capable of converting at leastsome of the carboxylic acid to a water-soluble carboxylate salt; (c)separating a solid phase comprising at least some of the drill cuttingspresent in the carboxylate salt-containing mixture formed in step (b)from a liquid phase comprising at least some of (i) the carboxylate saltand (ii) the oil-based drilling mud present in the carboxylatesalt-containing mixture and (iii) the water present in the aqueous basesolution; and (d) separating an oil phase comprising at least some ofthe oil-based drilling mud present in the liquid phase from an aqueousphase comprising at least some of the carboxylate salt and water presentin the liquid phase, the oil phase being denser than the aqueous phase.6. The method of claim 5 wherein the oil phase is separated from theaqueous phase in step (d) by removing the oil phase from beneath theaqueous phase.
 7. The method of claim 5 further comprising the step (e)of lowering the pH of the aqueous phase to convert at least some of thewater-soluble carboxylate salt to the carboxylic acid.
 8. The method ofclaim 5 further comprising the step (e) of lowering the pH of theaqueous phase to convert the water-soluble carboxylate salt to thecarboxylate acid, wherein the step (e) is conducted at ambient pressure.9. The method of claim 5 further comprising the steps of:(e) loweringthe pH of the aqueous phase to convert at least some of thewater-soluble carboxylate salt to the carboxylic acid; and (f)separating a modified aqueous phase comprising at least a portion of thewater present in the aqueous phase from an organic phase comprising atleast a portion of the carboxylic acid formed in step (e).
 10. Themethod of claim 5 further comprising the steps of:(e) lowering the pH ofthe aqueous phase to convert at least some of the water-solublecarboxylate salt to the carboxylate acid; (f) separating a modifiedaqueous phase comprising at least a portion of the water present in theaqueous phase from an organic phase comprising at least a portion of thecarboxylic acid form in step (e); and (g) using at least a portion ofthe carboxylic acid separated in step (f) in step (a).
 11. The method ofclaim 5 further comprising the steps of:(e) lowering the pH of theaqueous phase to convert at least some of the water-soluble carboxylatesalt to the carboxylic acid; (f) separating a modified aqueous phasecomprising at least a portion of the water present in the aqueous phasefrom an organic phase comprising at least a portion of the carboxylicacid formed in step (f); and (g) using at least a portion of thecarboxylic acid separated in step (f) in step (a), wherein steps (a)-(g)are conducted at ambient pressure.
 12. The method of claim 5 wherein theoil phase is separated from the aqueous phase in step (e) by removingthe oil phase from beneath the aqueous phase, the method furthercomprising the steps of:(e) lowering the pH of the aqueous phase toconvert at least some of the water-soluble carboxylate salt to thecarboxylic acid; (f) separating a modified aqueous phase comprising atleast a portion of the water present in the aqueous phase from anorganic phase comprising at least a portion of the carboxylic acidformed in step (f); and (g) using at least a portion of the carboxylicacid separated in step (f) in step (a), wherein steps (a)-(g) areconducted at ambient pressure.
 13. The method of claim 5 wherein theaqueous base solution employed in step (b) comprises at least about 1weight percent potassium calculated as KCl.
 14. The method of claim 5wherein the carboxylic acid employed in step (a) is selected from thegroup consisting of caprylic acid, capric acid, and mixtures thereof.15. The method of claim 5 wherein the carboxylate salt-containingmixture formed in step (b) has an aqueous phase having a pH above
 7. 16.A method for cleaning a mixture comprising drilling cuttingscontaminated with an oil-based drilling mud, the method comprising thesteps of:(a) contacting the mixture with a carboxylic acid; (b)contacting the carboxylic acid-containing mixture formed in step (a)with an aqueous base solution capable of converting at least some of thecarboxylic acid to a water-soluble carboxylate salt; (c) separating asolid phase comprising at least some of the drill cuttings present inthe carboxylate salt-containing mixture formed in step (b) from a liquidphase comprising at least some of (i) the carboxylate salt and (ii) theoil-based drilling mud present in the carboxylate salt-containingmixture drilling and (iii) the water present in the aqueous basesolution; and (d) lowering the pH of the liquid phase separated in step(c) to convert at least some of the water-soluble carboxylate salt tothe carboxylic acid.
 17. The method of claim 16 wherein step (d) isconducted at ambient pressure.
 18. The method of claim 16 furthercomprising the step (e) of separating an aqueous phase comprising atleast a portion of the water present in the aqueous base solution froman oil phase comprising at least a portion of (A) the carboxylic acidformed in step (d) and (B) the oil-based drilling mud present in theliquid phase.
 19. The method of claim 16 further comprising the step (e)of separating an aqueous phase comprising at least a portion of thewater present in the aqueous base solution from an oil phase comprisingat least a portion of (A) the carboxylic acid formed in step (d) and (B)the oil-based drilling mud present in the liquid phase, wherein the oilphase is separated from the aqueous phase in step (e) by removing theoil phase from beneath the aqueous phase.